Simultaneous detection of atmospheric CO and CH4 based on TDLAS using a single 2.3 μm DFB laser.

A laser-based spectrometer with a physical size of 60× 30 ×25 cm3 has been developed to continuously monitor CO and CH 4 in atmosphere based on tunable diode laser absorption spectroscopy (TDLAS). Two neighboring lines of CO and CH 4 around 2.3 μ m were selected as candidates for simultaneous measurement by a single diode distributed feedback (DFB) laser. A special Herriott-type multipass absorption cell, with a 72 m optical path length, was designed and used to enhance the absorption signals of sample gases. Normalized wavelength modulation spectroscopy was applied to improve the sensitivity and robustness of the spectrometer and it was implemented on a home-made electronic system based on field programmable gate array (FPGA). Meanwhile, the electronic system controlled the temperature and current of DFB laser with the precision of 0.01 °C and 40 ppm. The 2nd-harmonic signals normalized by the corresponding 1st-harmonic signals for both CO and CH 4 are of high linear response to their concentrations in the range of 0.046–4.6 ppm and 0.487–48.7 ppm, respectively. According to the Allan variance, respective minimum detection limits for CO and CH 4 are 0.73 ppb and 36 ppb at 122 s and 137 s. As an application example, the spectrometer has been validated through real-time and in-situ measurement of atmospheric CO and CH 4 for 48 h. Unlabelled Image • A compact laser-based spectrometer has been developed to monitor atmospheric CO and CH 4 using a single DFB laser emitting at 2.33 μm. • A special Herriott-type multipass cell combined with FPGA system was designed and used to improve the sensitivity and compactness of the system. • The normalized WMS-(2 f /1 f) technique was employed to achieve high robustness of spectrometer. • The spectrometer has been validated for real-time and in-situ measurement of atmospheric CO and CH 4 for 48 h. [ABSTRACT FROM AUTHOR]